1. Field of the Invention
The present invention relates to an improved buckle involved in a child-restraining device for safely securing child in a vehicle and, more particularly, to an improved buckle for safety seat belts exclusively adapted to children in motor-vehicles which has a simple structure and enables an easy buckling operation for locking and releasing the devices.
2. Description of the Prior Art
In recent years, the use of a safety seat belt has been recommended or rather compulsorily required for seat occupants in motor-vehicles in many countries for preventing their injury or physiological damage caused by a traffic accident. Thus, various kinds of safety seat belts have been developed for drivers and their fellow passengers of motor-vehicles. These safety seat belts are designed chiefly for adult passengers and thus are not suited for child passengers because children are much smaller in body weight and size such that they cannot be entirely restrained with a safety seat belt designed for adults and thus may be thrown out of their seats in the case of a sudden stop or accident. Besides the ordinary safety seat belts designed for adult passengers, various kinds of child-restraining devices have been also developed hitherto, which are of the type adapted to restrain a child's body with a safety seat belt. These devices are usually placed on a seat in a motor-vehicle for holding the child with the safety seat belt. Among the child-restraining devices developed heretofore, those providing a childs seat in a smaller size which just fits the child's body and containing a plural of safety belts has now become popular and meets the requirements that child passengers are entirely restrained a the plurality of safety belts so that the impact force exerted at the time of an accident to the child passengers may be dispersed by the plurality of safety belts supporting the childs's body at several points. Thus, the prior art child-restraining devices include those having 2-, 3-, 4- and 5-point supporting belts among which, for example, a child-restraining device having 5-point-supporting belts can support a child's body at he crotch, both knees and both shoulders. Such a device is now widely employed. In such conventional child-restraining devices, those having 4- or 5-point-supporting belts comprise a waist belt using a 2-component buckle and shoulder belts stitched thereto, or shoulder belts having a ring attached to the front ends thereof by stitching and a waist belt inserted into the ring. Typical examples of the prior art child-restraining devices are disclosed, for example, in Japanese UM Publn. No. 57-2197, U.S. Pat. No. 4,457,052, Japanese Laid-open UM Appln. No. 60-192942 and U.S. Pat. No. 4,062,091. However, the prior art child-restraining devices having 4- or 5-point-supporting belts have some inherent problems. Thus these devices are complicated in structure and troublesome in their locking and releasing operations.
For example, a child-restraining seat disclosed in the above-mentioned Japanese UM Publn. No. 57-2197 is of a type having 3-points-supporting belts, wherein shoulder belts 7a and 7b are separately fastened, as shown in FIG. 1, to a T-shaped pad 10 capable of protecting the abdomen of a child passenger. The front ends of the shoulder belts 7a and 7b are connected together to a tongue 11 which is engageable with a buckle 12 mounted to the front lower part of a child seat 1. The buckle assembly consisting of the tongue 11 and the buckle 12 used in this seat utilizes an ordinary buckle for conventional safety seat belts for adult passengers. On practical use of this child seat, a child passenger must pass his/her head between the shoulder belts 7a and 7b which creates an unpleasant feeling for the child, making the seat troublesome in operation. A buckle for a child seat having 3-point-supporting belts as disclosed in the aforesaid U.S. Pat. No. 4,457,052 and a child-restraining device having 5-point-supporting belts as seen in Japanese Laid-open UM Appln. No. 60-192942 were devised to overcome the above-mentioned drawback. A new 3-component buckle not having been used in this art was developed therein for safety seat belts for children so that the belts can be fastened or unfastened without the necessity of passing the beltwearer's head between both shoulder belts.
For example, the buckle disclosed in Japanese Laid-open UM Appln. No. 60-192942 is a 3-component buckle wherein a combination of two tongue members is engageable with one buckle in such a manner that a tongue member 42 is inserted at the front end 42 thereof into an opening 50 of another tongue member 46 and the front end 42A of the tongue member 42 is then engaged with a buckle 54. The mechanism of the buckling operation in case of using this buckle is of the same type as used in an ordinary 2-component buckle. Thus, the use of this buckle is troublesome and difficult for children since the buckling operation has to be carried out in a specific sequence, i.e. by first combining the tongue member 42 with the tongue member 46 prior to the actual buckling operation.
On the other hand, the 3-component buckle disclosed in U.S. Pat. No. 4,457,052 has a unique structure and is featured as shown in FIGS. 4-6, by such a structure that a pair of hasps 30 and 32, to which over-the-shoulder straps 26 and 28 are fastened, respectively, through slots 38 and 40 formed in the hasps are engageable with a center plate 60 and a release plate 66 in the buckle body 36 in such a manner that bosses 68 formed on the release plate 66 protrude significantly through aperture 64 formed in the center plate 60 and enter in to openings 90 and 92 of the hasps 30 and 32, capable of receiving the load of the straps. In the locked state of this buckle, the bosses 68 protruding through the aperture 64 of the center plate 60 are engaged with the openings 90 and 92 of the hasps 30 and 32 whereby shoulders 94 of the bosses 68 abut against the edges of the openings 90 and 92 of the hasps 30 and 32 to block any reverse movement of the hasps in the outward unlocking direction while the other ends of the bosses 68 abut against the inside wall of the aperture 64 of the center plate 60 to engage the hasps 30 and 32 with the center plate so as to support the load of the straps. However, the bosses 68 are energized to enter in the locking position, i.e. into the openings 90 and 92 only by the resiliency of the compression springs 86, it is likely that the engagement between the bosses 68 and the openings 90 and 92 becomes so unstable as to cause disengagement when an unexpected impact load is applied to the buckle due to an accident. On actual use of the buckle, the two hasps 30 and 32 are inserted into a receiving slot 88 in any order of succession whereby each boss having a sloped surface 70, which is not parallel with the center plate 60, is brought into contact with the inserted hasp. In this case, the vector of the movement of the release plate acting at the contact point between the sloped surface and the hasp is not exactly vertical to the center plate 60 so that bore 84 and the edge of the release plate 66 tend to cause friction, as readily anticipated from FIG. 6, to disturb return of the release plate 66 to the original position. Thus, there is the problem that the function of the buckle becomes unreliable according to the manner of inserting the hasps into the receiving slot 88 of the buckle.
Thus, all of the prior art child-restraining devices using 2-, 3-, 4- and 5-point-supporting belts in combination with 2-, 3- and 4-component buckles involve problems, particularly in that the function of the buckle is unstable, the engagement of the buckle with the tongue plates on the front end of the belts must take place in a fixed sequence, and the weight of the deivce is so heavy as to make the buckling operation complicated and troublesome. From the viewpoint of protecting child passengers from injury or physiological damage caused by accident, therefore, there is a great demand in the automobile industry for developing a new type buckle for child-restraining devices devoid of the above mentioned drawbacks seen in the conventional child-restraining devices.